In 2017, Spark Therapeutics licensed technology from nonprofit organization Genethon that the company’s scientists hoped would make gene therapy possible for treating Pompe. The inherited lysosomal storage disease causes the sugar glycogen to build up in muscles and organs such as the heart, impairing their function. Now Spark has data in mice that are encouraging enough for the company to initiate a phase 1/2 trial in people next year, Spark said today.

Pompe is caused by mutations in the gene that makes the enzyme acid alpha-glucosidase (GAA). Patients generally receive infusions of GAA every two weeks to control the disease, but Spark’s goal is to be able to replace that standard of care with a one-time gene therapy dubbed SPK-3006. They tested the gene therapy in mouse models of Pompe by comparing it to GAA that’s normally expressed in either the liver or in muscles.

They found that the gene therapy produced a better therapeutic response than either form of native GAA did. The animals were followed for 10 months after receiving the gene therapy, and during that time they didn’t experience any toxicities, the company said. What’s more, the GAA resulting from the gene therapy was better at restoring muscle strength than regular infusions of enzyme replacement therapy. Spark presented the data at the 23rd International Congress of the World Muscle Society in Argentina on Saturday.

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“Early preclinical data suggest sustained plasma levels of GAA facilitate greater uptake into muscle tissue throughout the body, efficient clearance of glycogen, as well as improved restoration of GAA muscle strength when compared to standard of care,” said Federico Mingozzi, Ph.D., chief scientific officer at Spark Therapeutics, in a statement. He added that because the gene therapy induces GAA production in liver cells, rather than in muscle, Spark’s scientists believe it will be less likely to produce dangerous immune responses.

Spark generated investor enthusiasm last December for its first FDA-approved gene therapy, Luxturna, to treat an inherited eye disease. The company is also working on gene therapies to treat the blood disorders hemophilia A and B. Spark recently posted positive data from a human trial of its hemophilia B gene therapy, which it’s developing with Pfizer, but it’s having a rougher time with its hemophilia A treatment. In August, news that a patient in a phase 1/2 trial ended up in the hospital with an immune response to the treatment sent the company’s shares down 30%.

Spark may have to contend with some competition in the market for new Pompe therapies. Startup Avrobio is also moving a gene therapy for Pompe through preclinical trials. It recently raised $100 million in an over-subscribed IPO.

Spark has already conducted a meeting with the FDA to discuss its clinical trial plan for SPK-3006, it said. It will enroll adult patients with Pompe in both the U.S. and Europe, and the company currently maintains full commercial rights to the gene therapy worldwide.